Cold injury

　　definition

　　Cold damage mainly refers to an agrometeorological disaster in which the temperature of tropical and subtropical crops is not lower than 0℃ during the winter growth period, and the physiological function of crops is impaired due to the temperature drop, resulting in yield reduction and even death.

　　brief introduction

　　Cold damage mostly occurs in South China, which is often affected by cold air in winter, resulting in intense cooling, which is seriously harmful to the main tropical and subtropical cash crops in South China, such as bananas, lychees, longan, sugar cane and rubber. Damage to tropical crops caused by low temperature. Mainly occurs in winter. Generally, the lowest temperature is around 10℃, which has been slightly affected, and it will be seriously affected at around 4 ~ 5℃. The symptoms of different crops are different. After the rubber tree is damaged, the tender tip of the terminal bud leaves is scorched, and the branches or trunks burst, dry up and the roots die. Coconut leaves withered, fruit withered and even the whole plant died. Cold damage of tropical crops can be divided into radiation type and advection type according to weather characteristics. The former is caused by radiation cooling in sunny and calm nights under the control of cold high pressure after the cold front passes through the border; The latter is caused by strong cold advection, long duration, low temperature and high wind speed, which generally lasts for 10 ~ 20 days. When the average temperature is below 10℃, rubber trees will die in large numbers.

　　Defensive countermeasures

　　The main measures to prevent winter cold damage are to seek advantages and avoid disadvantages, and to combine avoidance, resistance and prevention.

　　"Avoidance" means to stagger the peak period of cold injury and the sensitive period of vegetables by adjusting the cultivation season of vegetables according to the different characteristics of their ability to resist cold injury at different growth stages. Warm-loving vegetables should be planted on the flat land or hillside with sunny leeward, and avoid planting in valleys, depressions or hilltops with sunny leeward.

　　"Resistance" means breeding varieties with strong cold resistance. According to relevant research reports, under the same cold stress, the yield reduction of vegetable varieties with strong cold tolerance can be reduced by more than 30% compared with those with the same type and the same maturity. Therefore, we should focus on improving the cold resistance of vegetables in cultivation techniques. Studies have shown that the cold tolerance of plants to cold injury depends on the amount of carbohydrates in plants before cold injury, the consumption rate of respiratory substrates and the freshness of water in protein. Therefore, measures such as water and fertilizer regulation should be taken to promote the growth of vegetables and increase the "material reserve" of plants before the occurrence of cold injury. Adequate nitrogen-based fertilizer can promote early growth and rapid growth of vegetables, increase dry matter accumulation, and high potassium level is beneficial to strong stalks, increase sugar accumulation in cells, and improve the coldness of vegetables. In addition, phosphorus, silicon and calcium fertilizers also have significant effects on improving cold resistance. After the cold injury, once the plants come back to life, the soil should be loosened in time, the grass should be reduced and the available nitrogen fertilizer should be applied in pieces, supplemented by phosphorus and potassium fertilizer; According to the occurrence of pests and diseases and the growth of vegetables, choose the appropriate pesticides and dosage for prevention and control.

　　"Prevention" mainly includes the following methods: (1) Irrigation method: Irrigation the day before frost is expected. So as to protect the ground heat and improve the air temperature and humidity near the ground. If possible, spray water on the eve of frost, because the water temperature is higher than the air temperature (when the air temperature is 0℃ in the first frost period, the water temperature is generally about 15℃). When water condenses on crops, it will release heat, slow down the temperature in the plant, and the frost prevention effect is better. (2) Covering method: Covering crops with straw, film, etc. can not only prevent the attack of cold air outside, but also reduce the loss of ground heat, and generally increase the surface temperature by 1-3℃. (3) Fertilization method: applying manure, compost and plant ash in the field 3-4 days before frost can not only increase soil temperature, but also increase aggregate structure and improve soil fertility. (4) Wind barrier method: Before the frost comes, wind barriers are set on the ground of crop fields to stop the cold wind and reduce the cold damage. (5) Smoking method: it can produce a large amount of cigarette butts and give off a certain amount of heat, so that the air near the ground can be raised by 1-2℃. But this method will pollute the atmosphere, but it is suitable for short-term use in valuable seedling fields.

　　(Source: China Xingnong Network Editor: Sun Wei)